The present invention relates to a coil spring positioner. The present invention also pertains to a compressor for vehicle air-conditioning systems having the spring positioner.
Generally, existing structures for positioning spring ends include an annular groove. A stopper ring is fixed in the annular groove to project inward. One end of a coil spring abuts against the projecting part of the stopper ring, which positions the coil spring.
In a compressor having the above-described structure, as shown in FIG. 12, a crank chamber 203 is formed between a front housing member 201 and a cylinder block 202. In the crank chamber 203, a drive shaft 204 is supported by the front housing member 201 and the cylinder block 202. The cylinder block 202, which constitutes part of the housing, includes a plurality of cylinder bores 202a. A piston 206 is accommodated in each cylinder bore 202a.
In the crank chamber 203, a swash plate 205, which serves as a drive plate, is supported by the drive shaft 204 to integrally rotate and to incline with respect to the drive shaft. The swash plate 205 is coupled to a lug plate 217 through a hinge mechanism 216, and the lug plate 217 is fixed to the drive shaft 204. Each piston 206 is coupled to the swash plate 205 through a pair of shoes 222. A valve plate 207 is located between the cylinder block 202 and a rear housing member 208.
The rotation of the swash plate 205 is converted into reciprocation of each piston 204 through the corresponding pair of shoes 222. The reciprocation compresses refrigerant gas that is drawn to each cylinder bore 202a from a suction chamber 209 through the valve plate 207 and discharges compressed refrigerant gas to a discharge chamber 210.
A bleed passage 224 connects the crank chamber 203 to the discharge chamber 210. A control valve 218 is located in the bleed passage 224 and adjusts the flow rate of refrigerant gas. The difference between the pressure in the crank chamber 203 and the pressure in the cylinder bore 202a is varied by the control valve 218. The inclination angle of the swash plate 205 is varied in accordance with the pressure difference, which controls the displacement of the compressor.
The variable displacement compressor of this kind is coupled to an external drive source Eg such as vehicle engines through an electromagnetic clutch 223.
A support spring 212 abuts against the rear end of the drive shaft 204 through a thrust bearing 211. The support spring 212 is a cylindrical coil spring. The support spring 212 urges the drive shaft 204 axially. The support spring 212 prevents chattering of the drive shaft 204 in the axial direction due to measurement error of the parts. The force of the support spring 212 causes the drive shaft 204 to contact the thrust bearing 211.
A center bore 213 is formed substantially in the center of the cylinder block 202. A first annular groove 214 is formed in the center bore 213, and a stopper ring 215 is fitted in the annular groove 214. The support spring 212 engages and is located between the rear surface of a race 211a of the thrust bearing 211 and the stopper ring 215. In other words, the rear end 212a of the support spring 212 is positioned with respect to the cylinder block 202 by abutting against the stopper ring 215.
A second annular groove 220 is formed in the drive shaft 204 between the swash plate 205 and the cylinder block 202. A stopper ring 221 is fitted in the second annular groove 220. A limit spring 219 engages and is located between the rear surface 205a of the swash plate 205 and the stopper ring 221. The limit spring 219 is a cylindrical coil spring. The limit spring 219 resists a force that urges the swash plate 205 toward the rear housing member 202. When the limit spring 219 is compressed to its minimum length, the swash plate 205 is positioned at its minimum inclination angle. The rear end 219a of the limit spring 219 is positioned with respect to the drive shaft 204 by the stopper ring 221.
In the prior art spring positioners of FIG. 12, the position of each spring end is determined by a stopper ring. Accordingly, annular grooves for securing the stopper rings are required.
In the compressor of FIG. 12, spaces for the annular grooves 214, 220 for installing the support spring 212, the limit spring 219, and the stopper rings 215, 221 are limited. That is, large spaces are not provided between the race 211a and the stopper ring 215 or between the swash plate 205 and the stopper ring 221. To fully meet the force requirements of each spring 212, 219, the springs 212, 219 must be made of wires having a relatively large diameter. However, since the spaces for the springs 212, 219 are relatively small, springs made of relatively small-radius wires are actually used. Therefore, the springs 212, 219 may not have the desired operating characteristics.
A compression load in the direction of the axis of the drive shaft 204 is continually applied to the springs 212, 219. The support spring 212 is supported and compressed between the race 211a and the stopper ring 215. The limit spring 219 is supported and compressed between the swash plate and the stopper ring 221. Therefore, radial movement of each spring 212, 219 is limited.
If the compression load is reduced, each spring 212, 219 radially moves as the drive shaft 204 rotates. As a result, each spring 212 repeatedly contacts the inner surface of the center bore 213 and peripheral surface of the drive shaft 204. This generates noise and vibration and wears the springs 212, 219, which shortens the life of the compressor.